Urethane cross-linked poly(oxyethylene)/siliceous nanohybrids doped with Eu3+ ions Part 2. Ionic association

Abstract

Fourier transform mid-IR and Raman spectroscopies were employed to investigate the anionic local surrounding in sol–gel derived organic/inorganic materials–monourethanesils–incorporating europium triflate, Eu(CF₃SO₃)₃. The hybrid framework of these xerogels contains short methyl end capped polyether segments grafted to a siliceous network through urethane cross-links. Samples with compositions ∞ > n ≥ 10 (where n indicates the ratio of (OCH₂CH₂) moieties per lanthanide ion) were examined. The spectral data obtained provide conclusive evidence of the presence of “free” and weakly coordinated CF₃SO₃⁻ ions located in two distinct sites in the whole range of salt concentration analyzed. At n = 30 and 10, along with these species, two new anionic configurations, assigned to contact ion pairs and “cross-link separated” ions pairs, emerge. Two-dimensional correlation spectroscopic analysis allowed to clarify the number of components present in two critical bands containing strongly overlapped spectral profiles. The number of anionic environments found in the m-Ut(750)_nEu(CF₃SO₃)₃ family confirms the rich coordinating possibilities offered by polymer systems incorporating trivalent triflate salts.